1. Field of the Invention
This invention relates generally to communication systems, and, more particularly, to wireless communication systems.
2. Description of the Related Art
In the field of wireless telecommunications, such as cellular telephony, a typical system 100, as shown in FIG. 1, is a hierarchical architecture and includes a plurality of base stations 130 (e.g., Node Bs) distributed within an area to be serviced by the system. Various access terminals 120 (ATs, also known as User Equipment (UE), mobile devices, and the like) within the area may then access the system and, thus, other interconnected telecommunications systems, such as a publicly switched telephone system (PSTN) 160 and a Data network 125, via one or more of the base stations 130. Typically, an AT 120 maintains communications with the system 100 as it passes through an area by communicating with one and then another base station 130, as the AT 120 moves. The AT 120 may communicate with the closest base station 130, the base station 130 with the strongest signal, the base station 130 with a capacity sufficient to accept communications, etc. The base stations 130, in turn, communicate with a Radio Network Controller (RNC) 138, which communicates with a Packet Data Serving Node (PDSN) 164 in a core network 165. Each RNC 138 and PDSN 164 is capable of supporting a plurality of base stations 130. Thus, as an AT 120 moves and communicates with different base stations 130, it may also communicate with different RNCs 138 and PDSNs 164.
The wireless link between the ATs 120 and the Base Stations 120 is typically referred to as the radio link, and in systems such as the Universal Mobile Telephone System (UMTS), much of the coordination of the radio link is handled by the RNCs 138 in a relatively centralized manner. For example, hand-offs of the ATs 120 from one base station 130 to another is determined by the RNCs 138. Similarly, owing to their proximity to one another, the base stations 120 can generate signals that interfere with one another. In some applications, the RNCs 138 control the transmissions of the various base stations 130 to reduce or minimize this type of interference.
However, the industry intends for UMTS to evolve away from the use of RNCs 138 with a distributed Radio Resource Management (RRM) architecture. The complexity of hand-offs and interference mitigation increases in the distributed RRM architecture, as the RRM functions are located at different physical locations. Moreover, the conventional distributed RRM architecture may not permit coordination of multiple node-Bs during multicast/broadcast transmissions, e.g. transmissions according to Multimedia Broadcast Multicast Service (MBMS) Thus, conventional distributed RRM architectures may not achieve the well known advantages of macro diversity combining of signals from different node-Bs at each mobile unit that receives the multicast/broadcast transmission.